Cathode-ray oscilloscope



Jan. 18, Q W HANSELL 4 CATHODE-RAY OSCILLOSCOPE Filed Oct. 1l, 1944 l J AAAAAAAAAAAAA vv 1 vvvvvvvvvyv l//f'O AMPLIFIER JAN /G/VA L /NPUT F POM EA DA R PE' C E VER m6 R WW@ 0N MNM@ WM mace s G 5 k l E e y LT mgm L ESM @wf L+. MPN Q E S G,

l L L n. Y Rs mm y. 5 WH M N. 1w /U m l E T .C T N Y A m /f m Y C B \J\JJ JSQ AV .D h m m5/@0^ l] )V7 NNNT ,J MEM R il) wmew I, my? `|f G. lll 6 A 0 xm uw wr 4U /F LP 0 AN R Mfr N/ fw mwsw s crwpw "light 'response of i `j`Another,` `object f teristics in ffoscilloscop'es analogous -to frequency Patented Jan. 1s, 1949 s PATENT OFFICE CATHODE-RAY OSCILLOSCOPE v ,u porationl of Delaware Application October 11, 1944, Serial No. 558,200

Thepresentinvention relates to improvements vinssystems employing cathode ray tubes for visibly indicating recurring electrical Waves.l

lLTheinvention finds `particular usefulness in :radio locating. systems' employing short duration ipulses-Whichwhen reected from an object to -be;detectedf. appear as a modulation in intensity '.'or''as.a-deection of an electron beam on the 'cathode ray: oscilloscope. f However, it should llbec11nde`rstoodSithat the invention is not limited 'toi-the foregoingy use sinceit is applicable to any 'fsystem'em'ploying'a cathode ray oscilloscope for `visibly indicati'ng synchronously repetitive elecftrical'phenomenon.' i

u "One dimculty commonly experienced in radiov locatingsystems employing pulses of radio frequen'cywenergyv is that the 'maximum krange of detection is llimited by the receiver noise. The receiver noise hasa relatively large amount of energy because the pass band-is wide and thel nature off the system isI such that it has not `seemed possible tof employ pulse rate selectivity fafternal-detection for the purpose ofdiscrimif'nating between the desired pulse and noise. This follows from the fact that in such systems (sometimes referred' to as radar systemsrit is desired 'thatfall thef echo (reflectedlsignals from objects `I'o'verfav largefrange of distancesbe viewed at the -fsametima'- -Noisefandinterference, the peaks ofwhichoccur at-random time intervals, appears yoir-'theuorescent screen ofv the oscilloscope, thereby causing confusion to the viewer. It is therefore desirable toy 'provide a system which will' lift thereturning (echo or reflected) pulses outof noise and' interference to thereby providey -a clear distinction betvveenv desired signal pulses and undesired noise and interference.v

I`llt-fis :an 'ob'ject of the present invention to obl`tain.Ianimprovedvisignal-to-noise ratio in the u the vscreen of 'a cathode ray.

oscilloscope: `1

is to obtain response charac- `selectivityinconventional electrical circuits and '-'analogousftoi pulse. rate' -selectivity in pulse com# -munications[systems.

ffurtherobject is to obtain a regenerative jtimingflandlfrequency 'selective 'response charl'acteristic acathode ray oscilloscope over a broad ranger ofA repeating time .intervals '-1 Inf'one typical form of 'radar signal presentajjtion'bymeans ofA ani' oscilloscope, the transmitter pul's'elbauses-the cathode rayf beam' to start mov- Fing at a uniformrate 'one idire'ctionf across the "uorescenttfscreenfwhile returning reected l -i 19 claims. (ci. 315-30) i `waves and noise cause deflections of the beam atright angles to the uniform sweep.- In this manner deflections or pipsf due to returning Waves reected froman object have a position along the scanning line which is a measure of the distance to the object; This is called type A indication, in the radar art.

In another formof radar signal indication the radarsystem rotates and sends and receives beams in a succession of directions. The oscilloscope electron beam isi-.hen made to deect from a central point at a uniform rateand in ya direction corresponding to the rotational position of the system. The returning reflected `waves andthe noise then modulate the intensity of the electron stream. This type of indication presents a map of the area around the radar system as a center and is called plan-position indication, or PPI. r

In either type of indication, the presence of reecting objects isindicated by an increase in the -light emanating from certain areas of the fluorescent screen,land in both cases the noise also tends to produce light which makes it hard to distinguish'weak reflected waves.

The present invention makes it possible to ydistinguish reected waves from noise downv to much lower values of the reflected waves by making each area ofthe uorescent screen respond more and more strongly in production of light the more persistently it is struck by increased electron beam currents due to the reflected waves which repeat at a xed or only slowly 'moving part of the screen.

This is accomplished by causing the noise to be balanced in such a Way as to cause each area of the screen which is aected only by the noise to remain. at a relatively low potential whereas addition of current to any one area by the recurring effect of Waves reflected from an object will cause this one area of the screen to rise in potential at successive time intervals in a manner to give 1 much increased output of light in response to the reflected waves as compared with the light due to noise alone.

For this purpose, means are provided to keep the uorescent screen at a relatively low potential and to cause areas responding to reflected Waves to increase in potential, due to the known tendencyfor secondary emission from bombardment of the screento cause the bombarded area to rise toward the potential of the second anode, as a result of which secondary electrons are pulled awayfrom the screen.

This phenomenon fwhich I utilize in the presnearest the screen) is held at a relatively low-` potential. The Whole area of the --screen will then tend to assume the saine potential as'the second anode within G or -100 volts.y yThis comes about because each small area'ofithscreeneitlfrer collects, or releases, electrons until the number ber released due to secondary emission, and pulled away, are equal. likely to be attained when the potential of the area of the screenlis' fi'ornlf() Ateilt() volts slower, withrespect to the`c`atl1o'de`, than-fthe: potential fof f theflsecond anode,A dependingtiup'ont. the-:releer tric eld conditions,position=of theareaand fits secondary emission characteristics. u f f Assuming now that* itliettdi'electric ,capacity of the screen to surrounding '-c'on'stantipot'ential objects l or to rgroundl fis muchf larger @than 1 its capacity tothe second anode'r-.We mayfaiter the `bombardir'ig electron current fis 'turned ic'ff, Nraise fthe second anode potential toav much higher; Value than before Withoutcausingea correspondinginw crease in screen potential. "Illiisl places :the :screen potential at a value which :is'l'ar :from vita equi Jlibrium .poteritial.zi/indian.4 electron fb'ombardm'ent.

The screen potentialsisnowmuch-'below ytice equilibriuml potential. Having establfisliedtthis -condition',if We nowf-illcw7 a small electron current to flow to and boinbard a small area of'rthe screen,' ythissn'lall ar'eafwill releasev more fsecondary electrons to ,bef pulled to the 'second anode .than :the numberof primaryelectrons. `The"resulting current erlow causes: thisfone :bombarded :areato'rise progressively infpotential toward the much higher equilibrium potential. 'l?l'1e'tp;:ten tial rise -is-accor'npanied 1 by a correspondingfprogressive increase fin' 'light' emission. As a conse- Vquence, the intensity ci light 4ernittedbeccrnes a 'functionfboth of electronbeamcurrentwto the yarca and Gf the me (1U-ringwhichv this current U50 ner. x-Aft'erfthe vsignal isremouedg-lightfsomrtiee flows. This is to'be contrasted-With thebehavior ofA OscilloscopesA as commonly'used- Where theilight `lintensity is primarilya function of .the-,beam current and relatively little afectedfby the:time during which this current? iloWs. f

.It may be noted uthatf as fthe-, onefbombarded area increasesinpotentiall under. bombardment,

it establishes a vstrong velectric:- fieldfbetweenitself i and surroundingareas f; This: electric# field acts in a' direction tending'toxdecreasefthebombardment 60 -ftlie fpresent inventionil-anclrfconventicnalfoscl area," or tot prevent its spreading;- Which ris-an: aid I to obtaining 'sharply `focussed lelectronfvbeams.

The ilimlt: of .increase Iin glightf'femission, in irecourse, be reached if the areafisbombarded .long

f enoughrto cause the potential-.of the area-'to'.reacli i theequilbrium potential. .-ln practice it'isfthereffore" desirable 'to solimite-the Iproduct.- of. current f and time of il-owv of current to any one indicating Yareafthat `only-signals which.. are considerablyV 70 a, second corresponding'rtwicemnsdntotf'15 f strongerethan noisencan :cause .thevequilibr-ium ,fpotentialto be reached.h 'f

- However, it is.r desirableftlfiatsignals-Which are considerably stronger'thanf noisefbe limited in-the amount of light' einissicn:they-:causessof that'ex- The equilibrium condition-` i's'? cessive light will not be produced and weaker signals will not tend to be masked by it.

All of these conditions are readily satisfied by proper design and adjustment of equipment to 5 utilize the present invention.

In the operation of the present invention, I arrange to bombard the screen Awith electrons whi-lerlreepingwthe seconde. nodegpotyential low received, and high during time periods when slg lnfals are to be received, so that the screen poteny -tial,en/.eraseslow in response to noise, but higher in response't signals added to the noise. For

arxcon'dition of operation, the noise meyeryflow level of average illuminafnovvfareceiviiig signal wave (such as a ,pulse)..,is.addedqto-5the noise, the beam current to a particular area on the screen will increase, vthusifinereasing the net flow of electrons from this area, as a result of which the averagechargring, and' discharginglncurrents moit'hecarearno lo'iger balance and'l'thelf. average; potentialifonstheiarea will rise. rfHence';the'remissionfo' lightzlirora this area'rwillflalso riseandincrease progressitielyliizth' Y :the vvapa'ssagess` oft. the :"beamifcurrents I The .noise .f pulses arefzrandom inltiniingianclf amplitudesanl `will cnot repeat f"consistently4 withwthe sameziampliz; tude` andati the 'tsame area,ont-tite@z 'screen .IiT'he 'signal pulseshowever, 4doioccunWithirnorelnearly i3() lthefsameamplitudezand repeatiatlequallytspaoed time 'intervalsrsand for this reasonrll ill! beijev-i dent that? fthe; areasofv-the screenewhichwshows the noise Swillinot be as:brightgas,thoseiotheriareas which have desired signal pulses repeatedly added Y toftheinoises The potential-1.0i therfanea on-ithe v screen receiving the jsignalpwand lutheflight: {emisi- 'sion from it; will :continuel toin-creasezuntilg forces 'intervene Vto slowsup and then-:stop'the rislceOn'e of theseiorcesfis the-decreasing-:secondaryzyemis- 1 -40 f 'sion' ratioE as the 'impact` potentialsciriseil and-ans'other, -force is ftheitendencywfor :atheiiel'ectrcnsein tithe screen:discharging-current; whilefthensecond anode potential:isrlowyltoebe pulledttowardrscrelen 1. areas. of-fhigher f poten'tial.-

'Ilie4 resultfeof vadidime a1 signal current itc noiseA current fiseto i jcausellan .fincreasedrligbt-f'ifrcrn -ar'eas .'-receivingythe `signal ;current;iwhoseffamount wincreasesag-,With ltimegrin fthe mannerfk analogousnto building'fuproi` current -V in ythefresonant output'circuit-oise'r class ampli,-

areae will, -persist for av time in tdecreasingrinten- Hsity, asfelectrons fromttherdischarging electron .spray discharge ther-areaThusboth theibuildup and' :decay yofliglitfl remission` are! analogous l to buildup Aandfclecayaoff:eurrentinietuned :icincuit 'in responsezto-` pulsesfoi: currentr-iepeated at the resonant'requency. r 1 am;

. It-'shouldbei'noteat this tiniest atfon Vl:ofthe differences between@ the :y oscilloscopeI ,f systemmof scope systems is that the oscilloscoperfofstlieeinuvention givesrincrea'sing light responsefatsufcessive,1repetitionsfaupitofa;pointf-where ,they-ltimesof .arise anddecaybeccmesfsoislowrastobefpbje tippmore nearly full obtainableresponsefatieachrreceived pulses.- It.i believed thatethe-presentlinlvention.@can-tolerate;artiqlefioeebuildeupa sde- .,ca,y,.to wit elf/ esci *fina values o perhapsijzbmf spondng to a maximum radar range of 50,000 meters, (31 miles), the improvementJ would theoretically approach 100 to 1 in amplitude, or 10,000 to 1 in power.

In this connection it may be noted that experience with ordinary radar systems has shown that the apparent signal-to-noise ratio increases very little. if at all, when the average transmitted power is increased by increasing the pulse rate. This is because signal and noise power effective at the oscilloscope screen increase together with increase in number of repetitions and there is no increase in timing or frequency selectivity. Using the present invention, however, the added timing selectivity makes possible an improvement in effective, or apparent, signal-tonoise ratio as the repetition rate is increased.

It should be understood that the foregoing theoretical explanations have been given merely for the purpose of exposition in order that the invention may be better appreciated. While these theoretical explanations are believed to be correct, they are not of necessity complete, nor does the operation of the invention dependupon their accuracy or otherwise.

The features of the invention and objects, other than those stated above, will appear from a reading of the following description which is accompanied by a drawing wherein:

Fig. 1 illustrates one embodiment of the invention applicable to a radio locating (radar) system, and

Fig. 2 illustrates a modification of Fig. 1 which has wider application and can be used for the purpose of visibly indicating repeating electrical waves.

In the two figures of the drawing, the same parts are represented by the same reference numbers.

Inasmuch as the system of Fig. 1 is to be used in connection with a radio locating (radar) system, it is believed to be helpful to give a short description of a well known typ-e of radar system with which this invention can be used. The radar system transmits pulses of radio frequency energy which are very short compared to the time intervals between them. During the transmission of these short pulses, it has been customary to cut-off or block the receiver of the radar system in order to prevent paralyzing the receiver. After the pulses have been sent, they will continue on straight paths until they strike an object, such as an airplane, from which they will be reflected or bounced back to the transmission point at which the receiver of the radar sys tem is located. These reflected `or echo pulses return to the receiver during the time interval between transmitted pulses. The time interval between the transmission of the original pulse and the reception of the echois observed or measured and translated into the distance to the object.

Turning now to the drawing, the cathode ray tube is shown as having a cathode K, rst and second grids GI and G2, a focusing anode A, vertical deflection plates V and horizontal deflection plates H, a second anode A', and insu-v lated iiuorescent screen S, and a light translucent conducting layer L which is laid over the screen S. The layer L may be placed over the outside of standard tube-s. Its purpose is to pro vide a relatively large dielectric capacity between itself and each area of the screen so that the potential of the screen will not follow variations in potential of the second anode A'. A viewing hood or light shade I0 is used to aid in viewing the visible indications on the screen. It is preferably connected to and held at the same low or zero potential as the translucent conducting layer L.

The vertical deflection plates V are connected to the output of va video amplifier Il whose control grid is connected to the output of a radio locating (radar) receiver. The translucent backing or conducting layer L is maintained at some relatively low and constant potential with respect to the cathode by means of connection I2. The second anode A is maintained at a potential which is positive relative to the cathode and is connected to the anode of the modulator tube I3. The horizontal deflection plates H are connected by means of leads Ill to the output of a synchronized scanning -current generator I5. Generator I5 is controlled from the output of a square wave pulse generator I which in turn is coupled to and controlled by the output of the radio locating (radar) transmitter.

By means of suitable adjustments of the radar system, the square wave pulse generator I0 produces a rectangular wave pulse whose duration is equal to the time it takes an originally transmitted pulse to travel the maximum range to an object to be detected and back to the original transmission point. Because of the fact that the synchronized scanning current generator I5 is coupled to the output of the pulse generator i0, the sawtooth wave produced by the scanning generator I5 will have a linear slope of a duration substantially identical with the duration of the square wave pulse produced by generator IS. The control grid and the cathode of the modulator tube I3 are connected by means of leads Il to the output of the square wave pulse generator from which it receives a negative pulse of a magnitude sufcient to block or cut-off the ow of current through the tube I3 for an interval of time corresponding to the duration of the output pulse from I6. In the interval between the end of the pulse produced by generator I6 and the beginning of the succeeding pulse produced by generator I5, the modulator tube I3 will conduct current. It will thus be seen that the second anode A which pulls secondary electrons from the screen S is keyed in potential by the modulator tube I3 synchronously with the horizontal scanning sweep from the generator I5 in such a way that the second anode A' has a low potential during idle periods but some much higher potential during the time of the scanning sweep. This follows from the fact that during the time the modulator tube I3 is conducting, which occurs in time intervals between pulses from the output of generator I6, the flow of current through this tube will produce an IR drop in resistor R of a value which will reduce the potential on the second anode A'; while during the time the modulator tube I3 is non-conducting, which occur-s during the time that the generator I6 is producing a pulse, there will be no iiow of current through resistor R and the potential on the second anode A will be a maximum. In the foregoing discussion it has been assumed that the focusing system has been so designed as to give focusing of the electron beam in the cathode tube when the potential of the second anode A is high and the potential of the screen S is fairly low. Consequently the electron stream from cathode K through first anode A will be a well dened spot tracing out a pattern in response to potentials on deflecting plates H and V Whenthepotentialon secondanode A 'ishigh,.

but willzbe more'or less'spread out over. the4 screen when thepotential. on. second anode A is low.

Under'the foregoing conditions, they screen as a Whole may be made to assume a relatively low potential4 but any area: of the screen S'whichis under the scanningspot tends to rise in potential toward the potential of the second. anode A'. This is because the impact ofthe beam at a particular area on the screen S Will cause secondary emission from'this. area, as a result of whichthe secondary electrons knocked out from the screen which are of negative charge flow to the second anodeA, thus leaving positive potentials on this screenl area andV causingv a rise in potential of this area. The area of the screen thusr struck by the electrons will rise toward a more positive potential Whose uppermost limit is near thepositive potential on the second anode4 A. During the intervals between the times theecho pulses can be received (that is, in those idleV intervals When there are no spots on the screen from echo signals)the screen potential on` each: elemental areavvill tend to decrease toward the value placed on the second anode A 'by thetube i3, which is now conducting. Because each'elemental screen area has dielectriccapacity to theunderlying'conducting layer L,;this capacity tends to accumulate a chargeV while the area is under the scanning spot and to lose this charge slowly after the scanning spot is passed by. The moreffrefquently eacharea isA passed; by by thesscanning` spot, the greater will be the-charge that is ac cumulated on this area-and the higher'willbethe potential onthis area, andthe brighter'4 vvillfbe the lightproducedwhile the spot is passing;

Itv willthus be' seen that the oscilloscope is regenerativein nature so as to emphasize signals which repeat at the'same place ony the screen and to make them much more distinguishable from receiver noise' and interference which does not repeat at thesame spot on the screen; Putting it in otherv wordstthe response to signals which repeat inthe same position on successivey scans is increased With respect to noise andinter; ference which occurs .in randomA positions. arrangement thus addsY a form of timing and pulse rate selectivity toiradar'systems equivalent to that obtainable byr pulse integrationv and regeneration in pulse communications systems.

In order to emphasize the effect of signal pulses with respect to totalV light in a` Type A indicating system I have shown a means tov modulate both the-position andthe intensity of electron beam current with the signal input. For this purpose the control electrode G1 is supplied with signal pulses, principally through'l bypass' condenser C, simultaneously'with application of the signals to one of the vertical'dei'le'cting plates V. For PPI indicationsV theY signalsl would, of course, beapplied only to the control electrode Gi.

Fig. 2` is a` modicationl ofv Fig; l. and diiers therefrom primarily in' the'. facty that the system of the invention' is now applicable to'enli'ancingV the light response characteristic of any periodi'- caily repeating synchronously controlled signal Wave form. It should be noted that'the vertical deection plates of the cathode ray tube of Fig. 2 arenot shown, .although .such plates `may be used in the tube andthe connection from such'platesl to the video amplifier maybe omitted: The signal from the receiver is-'now applied onlyto the first grid' Gi through a video4 amplifier Il, as in Fig; l. The'operation of the second anode This andthe screento provide an imp1oved.signal-to-v` noise-ratio in the light response.- of the. screen' is substantially the same as describedabovein.,

connection with Fig. l. The square; Wavepulse generator IB- of Fig. 2 is designed toy produce pulses during the time the signalA pulses from the receiver are appliedto the grid Gl, at which' time a pulse of negative polarity is suppliedto the grid. of tube l3-via leads i1 of such magnif tude as to bias the tube I3 to the cut-oir` condition. In the intervals between signal pulses;

thel modulator tube I3 is conductive andthe' anode.l potential causes a de-focused spray of electrons to charge the screen to low potentials.

VDuring the signal periods, it'will be obvious that' the screen area struckby theiocused beamfrisesf to higher and higher potentials-With successive passages of the spot.

An added feature of Fig. 2`is a coupling'back' from keying tube |3=toramplier tube I I in such a manneras. to increase the electron beam current in the cathode ray tube While thexpotential` of' its second anode A is low, so as to discharge potentials on the screen S more rapidly.

It should be understood that variousmodiiications mayv be made in the systems of'v Figs. l

and 2, Without departing from the spirit and.

scope of the invention. Forexample, the action of the potential on the second anode A can be reversed" so that the anode potential is made higherbetvveen signalperiods than during signal' and rapidly accelerating the modulated stream substantially solely during periods of modulation, Without changing the speed of deflection.

2. In apparatus including a cathode ray tube having a target area and means for developing an electron stream adapted to be projected toward the target area, thev method of operation which includes modulating the developed stream by signal energy, deecting the stream syn'- chronously Withsaid modulation, and accelerating the modulated and deflected stream substantially solely during periods of modulation', without varying the spe-ed of deflection.

3. The method of operating a cathode ray oscilloscope having a fluorescent target and a second anode, Which comprises applying periodically recurring signal waves to an electrode of said oscilloscope, raising the potential on said second anode during periods in Which said signals are being applied to said oscilloscope, and

vcausing a decrease in the potential on said on said second anode during periods in which said periodically recurring pulses are to be applied to said vertical deflection elements, and causing a decrease in said Voltage on said anode during intervals between said periods.

5. .The method of operating a cathode ray oscilloscope having vertical and horizontal deection elements, a iiuorescent screen, a beam intensity control electrode, and a second anode, which comprises applying periodically recurring pulses of energy of short duration compared to the time intervals between them to said vertical deflection elements, and to said control electrode,

synchronously applying a beam deflecting wave to said horizontal deflection elements, raising the voltage on said second anode during periods in which said periodically recurring pulses ar-e to be applied to said vertical deflection elements, and causing a decrease in said voltage on said anode during intervals between said periods.

6. The method of operating a cathode ray oscilloscope having a light responsive screen, a beam intensity control electrode, b-eam deflection elements, and a second anode, which comprises applying periodically recurring waves to said control electrode, synchronously applying a deflecting wave to said beam deection elements, and synchronously modulating the voltage on said second anode.

7. A system for visibly indicating periodically recurring electrical waves, including a cathode ray tube having a cathode, an intensity control electrode, a iirst anode, beam deilecting electrodes, a second anode and a light responsive target, a source of saw-tooth waves coupled to said beam deecting electrodes, a circuit for applying said periodically recurring waves to said intensity control electrode, and means under control of said circuit for varying the voltage on said second anode in substantial synchronism with the periods during which said waves are applied to said control electrode.

8. A system for visibly indicating periodically recurring electrical waves, including a cathode ray tube having a cathode, a first anode, vertical and horizontal pairs of deection electrodes, a second anode and a light responsive target, a source of sweep waves coupled to one pair of said deflection electrodes, a circuit for applying said periodically recurring Waves to said other pair of deflection electrodes for time intervals less than the total time, and means for synchronously raising the voltage on said second anode substantially solely during said time intervals.

9. A system for visibly indicating periodically recurring electrical waves, including a cathode ray tube having a cathode, an intensity control electrode, a rst anode, vertical and horizontal pairs of deflection electrodes, a second anode and a light responsive target, a source of sweep waves coupled to one pair of said deection electrodes, a circuit for applying said periodically recurring waves to said intensity control electrode and to said other pair of deflection electrodes for time intervals less than the total time, and means for synchronously raising the voltage on said second anode substantially solely during said time intervals.

10. In apparatus including a cathode ray tube having a cathode for producing an electron beam and a light responsive target area, a circuit for modulating the electron beam in accordance with signal energy, a pulse generator, a source of sweep waves under control of said pulse generator for deecting said beam, and an electron discharge device system under control of said pulse generator for accelerating the modulated beam substantially solely during periods of modulation and without affecting the operation of said source of sweep waves.

l1. In apparatus including a cathode ray tube having a cathode for producing an electron beam, alight responsive target, an anode located between said cathode and target, and a translucent backing adjacent said target but insulated therefrom, a circuit for maintaining said anode at a positive potential and said backing at a lesser potential lrelative to said cathode, a source of periodically recurring waves for modulating the electron beam, and an electron discharge device circuit under control of said source for raising the potential on said anode substantially solely during periods of modulation.

12. Apparatus in accordance with claim 11, characterized in this that said electron discharge device circuit includes a pulse generator and a vacuum tube under control of the output of said pulse generator', there being a connection from the output electrode of said vacuum tube to the anode of said cathode ray tube.

13. In apparatus including a cathode ray tube having a cathode for producing an electron beam, aiirst anode, beam deflecting electrodes, a second anode, a light responsive screen, and a translucent backing adjacent said screen but insulated therefrom, a circuit for maintaining said second anode at a potential which is positive relative to said first ano-de and said backing, a source of periodically recurring waves for modulating said electron beam in accordance with signals, a pulse generator under control of said source for generating pulses in response to the occurrence of said waves, a sweep source under control of the output of said generator, connections from said sweep source to said beam deflecting electrodes, and a vacuum tube having an electrode coupled to said second anode and having grid and cathode electrodes coupled to the output of said pulse generator, whereby the occurrence of pulses in the output of said pulse generator affects the conductivity of said vacuum tube and hence varies the potential on said second anode in synchronism with the modulation of said beam.

14. In an oscilloscope system comprising a cathode ray tube having a fluorescent screen, means for obtaining increasing light intensity per unit of signal current, with increasing average current flow to areas of the fluorescent screen of an oscilloscope comprising a signal input circuit for said tube, means to charge the areas to low potentials during selected repetitive time periods, and means responsive to signals in said input circuit in other time periods and responsive to current flow for charging the same areas to higher potentials.

l5. In an oscilloscope indicating system comprising a cathode ray tube having a cathode for producing a stream of electrons, a iluorescent screen, a backing layer, and an electrode positioned between said cathode and screen and normally maintained at a low potential relative to said cathode, means establishing a large dielectric capacity between said screen and back ing layer, a signal input circuit for said tube, means including said cathode and said electrode for spraying said screen with an unfocussed stream of electrons from said cathode during time periods not occupied by input signals, and means to scan portions of said screen with a focussed stream of electrons and to simultaneousi ly increase saidpotential on saidelectrode during portion and a portion with diverging sides, a

target locatedat the Widestend. ofy the envelope, axcathode near the other endof the envelope, a backing adjacent said target but insulated therefrom, a control electrode adjacent said cathode, a first anode ,near said cathode and i positioned vin the path of .the electron stream from said cathode tov said target, a second anode comprising a metallic coating on the diverging sides of said envelope, means for maintaining said second anedeatapositivepotential and said backing Yat a lesser potential relative to said cathoda'means coupled to-said control electrode for applying modulation thereto, and means for modulating the lpotential on said second anode in .synchronism with the modulation applied to saidcontrol electrode.

17. Inapparatus including acathode ray tube having a cathode, a .fluorescent screen, an anode located between said cathode and said screen, and a translucent backing located adjacent said screen but insulated therefrom, means for maintaining said anode at aY positive potential and said backing at a constant negative potential i relative to said cathode, means for applying signal energy `to stillanother `electrode of said cathode ray tube, and means for changing the potential `of said anode substantially solely during, periods in which signal energy is applied to said tube.

18.. In apparatus including a cathode ray tube havinga cathode, ra light responsive target and rst and second anodes located between said cathode and target,anda translucent backing adjacent said target but insulated therefrom, a circuit for maintaining said first and second anodes vat positive potentials and said backing,

at a-negative potential relative to said cathode, means for applying signal energy to still another electrode fot said .tube,1.and .meansfor changing the` potential of said. second anode .'relativeito said-cathode without substantially. changing. the potential of said iirst anode relative ,tossici cathode, substantially solely during periods -in which signal energy is applied to said tube.

19. In apparatus including a cathode ray tube having a cathode,- a target, and first and second anodes located between said cathode and. target,

a circuit for maintaining said first and second anodes at positive potentials relative to said cathode, acircuit'for modulating the electron stream developed by said cathode, and means for synchronously varying the potentialv on said Ysecond anode without substantially varying-the potential ofl said yiirst anode relative to i said .cathode CLARENCE W. HANSELL.

REFERENCES CITED The following references are of recordin. the file of this .patenti UNITED STATES PATENTS .Number Name Date 2,004,790 Hehlgans June 11, 1935 2,074,737 Wolff Mar. 23, 1937 2,081,942 Lubcke June 1, 1937 2,188,647 Busse Jan..30, 1940 `2,197,625 Teves et al Apr. 16, 1940 2,222,943 George Nov. 26, 1940 2,234,830 Norton Mar. 11, 1941 2,241,256 Gould May 6, 1941 2,313,967 Read, Jr. Mar. 16, 1943 2,353,810 Schrader et al. 'Nov. 28, 1944 2,369,631 Zanarini Feb. 13, 1945 FOREIGN PATENTS Number Country Date 426,706 Great Britain Jan. 5, 1934 503,893 Great Britain July 5, 1938 

